Gas turbine engines, and the devices that are powered by gas turbine engines, are limited in overall design and performance by mechanical, material, and thermodynamic laws. They are further constricted by the design limitations of the three elements that make up the baseline design of gas turbine engines: the compressor, the combustor and the turbine. In turbines for aircraft, these three engine sections are contained inside of the outer turbine casing and are centered on a load bearing drive shaft that connects the turbine (on the rearward portion of the drive shaft) with the compressor (on the forward portion of the drive shaft). Typically the drive shaft is a twin or triple spool design, consisting of two or three concentric rotating shafts nested one inside the other. The different spools allow the turbine assembly and the compressor assembly, each of which is connected to one of the spools of the drive shaft, to rotate at different speeds.
The turbine is optimized to run at one particular speed for combustion and thrust processes, and the compressor is optimized at a different speed to more efficiently compress incoming air at the inlet face and raise the air pressure to a significant point to where there is a pressure ratio differential, significant enough to provide combustion. Highly compressed air at ratios of 30:1 to 40:1 ignites when mixed with atomized fuel in the combustor. The difference in speeds of the spools is typically accomplished by reduction gears to accommodate the required speeds for combustion and propulsion operation.
The compressor assembly consists of numerous compressor stages, each of which is made up of a rotor and a diffuser, the number of stages dependent upon the total pressure ratio increase required to achieve combustion and produce the desired thrust. The rotor is a series of rotating airfoil blades, or fans (attached to the shaft), which converge the air, i.e., compressing the volume of air and increasing its velocity, on the intake side of the blade, by passing it into a smaller volumes (convergent channels between airfoil rotor blades) in each the rotor chamber. Adjacent to each rotor is a diffuser (or stator). The diffuser is a fixed, non-rotating disc of airfoil stators whose sole purpose is to reduce the air velocity from the rotor and increase the pressure. The diffuser slows the air down by passing it through divergent (expanding) channels between the airfoil stators, thus recovering the pressure. Upon entering the diffuser the air passes from a narrow opening on the intake side of the diffuser into a gradually enlarging chamber (diffuser) that slows the velocity and raises the pressure of the air. Each compressor stage is made up of a compressor rotor and a diffuser (stator) disc. There are as many stages of the compressor as are required to get the air to the required air temperature and compression ratio (in high performance aircraft turbines usually in between 12:1 to 30:1 dependent on combustor design, flight and speed envelope and turbine thrust requirements prior to entering the combustor.
In the combustor, the high pressure, high temperature, expanding air mixes in a swirl of hot vaporized fuel and ignites to form a controllable flame front. The flame front expands as it combusts, rotating and driving turbine blades as the flame front exits the engine. The turbine assembly consists of several sets of rotating turbine blades connected to the drive shaft and angled so that the thrust of the flame front causes the blades to rotate. The turbine blades, being connected to the drive shaft, cause the drive shaft to rotate and thus the compressor blades to rotate, consequently more air is compressed and the cycle starts all over again.
However, existing turbine designs are limited by their implementation of such drive shafts and, accordingly, there needs to be a movement of towards using and designing “shaftless” turbine engine systems. It is expected that future U.S. air dominance will see a proliferation of hypersonic propulsion systems and vehicles to power effectively and efficiently high speed strike weapons. Speed is rapidly becoming the new stealth, providing drastically reduced time-to-target for near real-time action in theatre and a very low probability of intercept. As the threats faced by the U.S. military push friendly forces further away from high value targets, the air war will require speeds in the range of Mach 5.0-8.0, to ensure timely and effective strike in an anti-access/area denial environment.